1. Field of the Invention
This invention relates in general to electronics and electromechanical equipment, and more particularly to such equipment that is susceptible to corrosion and other damage.
2. Description of Related Art
Many types of electronic and electromechanical equipment are susceptible to corrosion and damage. In particular, when moisture is present with electronic circuits and devices, corrosion tends to occur. In addition, during device processing and implementation, damage can occur to components thereof. The reduction and/or elimination of such corrosion and damage has been important to the operation and longevity of electronic and electromechanical equipment.
One type of equipment that is highly susceptible to corrosion is recording equipment. The functionality and operation of such equipment has become increasingly important, such that corrosion and other damage can have drastic consequences. For example, magnetic recording is a key and invaluable segment of the information-processing industry. While the basic principles are one hundred years old for early tape devices and over forty years old for magnetic hard disk drives, an influx of technical innovations continues to extend the storage capacity and performance of magnetic recording products.
Mass storage devices including magnetic disk drives have been important components of computing platforms. The magnetic disk drive typically includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm above the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly mounted on a slider that has an Air-Bearing Surface (ABS) between the slider and the rotating disk. The suspension arm biases the slider into contact with the surface of the magnetic disk when the magnetic disk is not rotating. However, when the magnetic disk rotates, air is swirled by the rotating disk adjacent to the ABS causing the slider to ride on a cushion of air just above the surface of the rotating magnetic disk. The write and read heads are employed for writing magnetic data to and reading magnetic data from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the write and read functions.
Unfortunately, corrosion often occurs in magnetic disk drives and heads due to the presence of moisture, which acts as a thin-film electrolyte in combination with oxygen and certain contaminants to drive chemical reactions. To protect against corrosion and damage, carbon-containing overcoats have been used on the disks and heads. Unfortunately, typical overcoats can inhibit the ability to scale the areal density higher because the thickness of the overcoat must be reduced accordingly. As the overcoat is thinned, it loses its ability to protect the disks and heads from corrosion and damage. For example, when overcoats are thinned to about two nanometers or less, the head and disk become particularly susceptible to corrosion and damage.
For HDDs, the type of environment in which the drive resides also significantly affects its performance characteristics. For example, since disk drive performance is determined largely by the rotational speed of the disks, this speed has increased over time. Much of the power dissipated by HDDs is due to drag from air in the HDD enclosure. At low speed, dissipation is due to viscous drag and the power (P) scales approximately according to the equationP∝ην2   (Equation 1)wherein:
η is viscosity and
v is velocity.
At the very high speeds and large Reynolds numbers inside HDDs, the power dissipation is largely due to form drag and the power scales approximately according to the equationP∝ρν3   (Equation 2)wherein ρ is the is the density of the gas in the HDD enclosure. Form drag as referenced above relates to drag forces on the spinning disk of the HDD that results from the separation of air near the disk surface. The Reynolds number is a dimensionless ratio of the inertial flow forces to the viscous forces within a fluid, here the environment in which the HDD resides.
Many approaches have previously been used for sealing magnetic disk drives and other electronics equipment to inhibit corrosion and/or to provide an environment that is otherwise beneficial to HDD operation. For example, HDDs have previously been sealed in a non-hermetic fashion to prevent particles from entering the drive using a breather filter to equalize pressure (e.g., as altitude changes). Typical seals employed for HDDs use polymers such as elastomer gaskets and adhesive tape. Unfortunately, these approaches do not prevent moisture from passing into the enclosures (HDDs) that they seal. For instance, the solubility of water in polymers is very high, resulting in high permeation rates for polymer seals. The permeation rate of a gas through a solid is given by the equationQ=DbPA/h   (Equation 3)with the permeation constant K given by K=Db and wherein:
Q is the permeation rate,
D is the diffusion coefficient,
b is the solubility,
P is the pressure difference across the solid,
A is the cross-sectional area of the solid, and
h is thickness of the solid.
Typical applications involve upwards of about 15 different seals for a single enclosure, with each seal being susceptible to permeation as a function of the above equation(s).
Other approaches to providing desirable sealing are typically difficult to implement and/or expensive. For instance, canning-type methods involving compressed polymers and complex geometry are not readily applicable to HDD implementations. Similarly, sealing approaches involving metal gaskets typically involve relatively high compression forces that are not applicable to typical HDDs, which do not exhibit the stiffness or other characteristics for accommodating large compression forces. Achieving such stiffness or other characteristics for HDDs and other electronic/electro-mechanical equipment would typically involve expensive and bulky enclosures.
The above-discussed issues have presented challenges to the manufacture and implementation of disk drives and other electronics equipment.